There are many times in industry when it is a requirement to measure the particle size characteristics of materials (often to check that a manufacturing process is operating correctly, or that materials that are to be input to a process are suitable). Processed slurries are an example of a kind of material that needs to be analysed in, for example, the mining and ore-extraction industry. In, for example, platinum refining it is common to have a slurry of ground and sieved ore and to want to ensure that the grinding and sieving operation is working properly. This will be taken as an example of a field where the invention has application, but should not be seen as being restrictive: the invention has applicability to many other fields.
A slurry is often far too concentrated to be passed through existing particle size distribution analysers (e.g. laser light scattering equipment). Slurries can be more than 50% solids whereas typical measurement conditions should be 1% or less solids. Up until now dilution of the slurry has been achieved by mixing a sample of slurry in a tank and then taking a sample volume of the diluted mixture. This process is slow: time needs to be allowed for the concentrated sample to be thoroughly mixed with the diluent (e.g. water). It is difficult to suspend large particles and when in suspension such particles have a tendency to differentially sediment. Furthermore, taking a small volume of a large volume of diluent with sample mixed in it has the possibility of large sampling errors: different sized particles mix in different ways, and simply taking out a bucket of mixture from a large tank of diluent plus sample can skew (or otherwise distort) measured particle size distribution significantly. Furthermore, after taking the sample from the diluted substance sample there is the problem of what to do with the remaining (vast majority) of the diluent plus sample. If the slurry/sample is toxic it may not be possible simply to pour it into a drain or river.